1. Field of the Invention
The present invention is related to very large scale integrated circuit chips and more specifically to a method for optimizing the operating parameters of a voltage regulator mounted on the surface of a very large scale integrated circuit chip package.
2. Prior Art
A chip or die is a substrate on which active and passive components of an integrated circuit are fabricated. In order to plug into a socket on a printed circuit board, the chip is mounted in a pin grid array (PGA) ceramic package. In prior very large scale integrated circuit (VSLI) chips the supply voltage at which the components on the chip operate is 5 volts. Newer products designed to operate in low power personal computers operate at 3.3 volts. In order to allow a chip that is designed to 3.3 volt specification to operate in existing systems that operate with 5 volts, voltage regulators with a 5 volt to 3.3 volt conversion capability are mounted on the surface of the PGA package.
U.S. Pat. No. 5,444, 298 for "Voltage Converting Integrated Circuit Package", granted on Aug. 22, 1995 to Schutz, describes an integrated circuit which is designed to operate at a low voltage (approximately 3.3 volts) to be utilized in a system designed for an integrated circuit which operates at a higher voltage level (approximately 5 volts). 5 volts supplied on an input pin of a package is converted to 3.3 volts which is distributed to the chip and used to power the chip. A multi-layer ceramic pin-grid array having a cavity-down configuration is disclosed. Attached to the outer surface of the package is a voltage regulator for converting a first operating voltage supplied from a printed circuit board or other higher level packaging into a second operating voltage which is utilized by a semiconductor integrated circuit contained within the package. Placing the voltage regulator on the exterior of the package helps thermal dissipation. A decoupling capacitor is shown attached to the outer surface of the package to reduce power distribution noise. A plurality of decoupling capacitors can be used in some applications to improve Vcc noise performance. A plurality of heat sinks are applied to the outer surface of the package to help maintain the semiconductor integrated circuit within a reliable temperature range. A plurality of pins or leads provide for electrical interconnection of input-output signals, power supply lines and ground supply lines, respectively, to the package from a printed circuit board.
The pins of the package are provided with the same "pinout" as a package for a functionally equivalent semiconductor circuit which is designed to be powered at a different voltage. In this way package can be simply plugged into a socket designed for a package of a functionally equivalent circuit but a circuit which is designed to operate at a higher voltage level. A pinout compatible version of the voltage converting integrated circuit package allows an integrated circuit which is designed to operate at a low voltage (approximately 3.3 volts) to be utilized in a system designed for an integrated circuit which operates at a higher voltage level (approximately 5 volts).
The response of a voltage regulator to changes in load is called the transient response, and the magnitude of the voltage deviations at the voltage regulator output is controlled in a particular application by the value of output capacitance selected. The output capacitor supplies current to load during the response and recovery time of the voltage regulator. On-package voltage regulation introduces unique requirements which must be met in the selection of the correct capacitors.
It is therefore desirable to provide optimum values for capacitors to improve the transient response of an on-package voltage regulator.
It is desirable to permit new parts operating at 3.3 volts to operate in printed circuit boards with either 3.3 volt or 5 volt wiring.
It is desirable to provide dual voltage operation of a integrated circuit chip package having an on-package voltage regulator.